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3.1.1 Why use session beans
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Session beans are a lot more than just business logic holders. Remember the EJB services we briefly mentioned in chapter 1 The majority of those services are specifically geared toward session beans. They make developing a robust, featurerich, impressive business logic tier remarkably easy (and maybe even a little fun). Let s take a look at some of the most important of these services. Concurrency and thread safety The whole point of building server-side applications is that they can be shared by a large number of remote clients at the same time. Because session beans are specifically meant to handle client requests, they must support a high degree of concurrency safely and robustly. In our ActionBazaar example, it is likely thousands of concurrent users will be using the PlaceBid session bean we introduced in chapter 2. The container employs a number of techniques to automagically
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Building business logic with session beans
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make sure you don t have to worry about concurrency or thread safety. This means that we can develop session beans as though we were writing a standalone desktop application used by a single user. You ll learn more about these automagic techniques, including pooling, session management, and passivation, later in this chapter. Remoting and web services Session beans support both Java Remote Method Invocation (RMI)-based native and Simple Object Access Protocol (SOAP)-based web services remote access. Other than some minor configuration, no work is required to make session bean business logic accessible remotely using either method. This goes a long way toward enabling distributed computing and interoperability. You ll see session bean remoteability in action in just a few sections. Transaction and security management Transactions and security management are two enterprise-computing mainstays. Session beans, with their pure configuration-based transactions, authorization, and authentication, make supporting these requirements all but a nonissue. We won t discuss these services in this chapter, but chapter 6 is devoted to EJB transaction management and security. Timer services and interceptors Interceptors are EJB s version of lightweight aspect-oriented programming (AOP). Recall that AOP is the ability to isolate crosscutting concerns into their own modules and apply them across the application through configuration. Crosscutting concerns include things like auditing and logging that are repeated across an application but are not directly related to business logic. We ll discuss interceptors in great detail in chapter 5. Timer services are EJB s version of lightweight application schedulers. In most medium- to large-scale applications, you ll find that you need some kind of scheduling services. In ActionBazaar, scheduled tasks could be used to monitor when the bidding for a particular item ends and determine who won an auction. Timer services allow us to easily turn a session bean into a recurring or nonrecurring scheduled task. We ll save the discussion of timer services for chapter 5 as well. Now that you are convinced you should use session beans, let s look at some of their basic characteristics.
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Getting to know session beans
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A session bean alternative: Spring
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Clearly, EJB 3 session beans are not your only option in developing your application s business tier. POJOs managed by lightweight containers such as Spring could also be used to build the business logic tier. Before jumping on either the EJB 3 session bean or Spring bandwagon, think about what your needs are. If your application needs robust support for accessing remote components or the ability to seamlessly expose your business logic as web services, EJB 3 is the clear choice. Spring also lacks good equivalents of instance pooling, automated session state maintenance, and passivation/activation. Because of heavy use of annotations, you can pretty much avoid XML Hell using EJB 3; the same cannot be said of Spring. Moreover, because it is an integral part of the Java EE standard, the EJB container is natively integrated with components such as JSF, JSP, servlets, the JTA transaction manager, JMS providers, and Java Authentication and Authorization Service (JAAS) security providers of your application server. With Spring, you have to worry whether your application server fully supports the framework with these native components and other high-performance features like clustering, load balancing, and failover. If you aren t worried about such things, then Spring is not a bad choice at all and even offers a few strengths of its own. The framework provides numerous simple, elegant utilities for performing many common tasks such as the JdbcTemplate and JmsTemplate. If you plan to use dependency injection with regular Java classes, Spring is great since DI only works for container components in EJB 3. Also, Spring AOP or AspectJ is a much more feature-rich (albeit slightly more complex) choice than EJB 3 interceptors. Nevertheless, if portability, standardization, and vendor support are important to you, EJB 3 may be the way to go. EJB 3 is a mature product that is the organic (though imperfect) result of the incremental effort, pooled resources, shared ownership, and measured consensus of numerous groups of people. This includes the grassroots Java Community Process (JCP); some of the world s most revered commercial technology powerhouses like IBM, Sun, Oracle, and BEA; and spirited opensource organizations like Apache and JBoss.
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